1. Field of the Invention
The present invention relates to a hollow-fiber filter module for use in water purifiers.
2. Description of the Prior Art
Hollow-fiber filter membranes possess excellent filtration performance and, therefore, have conventionally been used in water purifiers for the preparation of, for example, high-purity industrial water, potable water and sterile water for medical use.
Most conventional filter modules provided with a hollow-fiber filter membrane and intended for use in such water purifiers have had a structure in which hollow fibers for filtration use are disposed within a cylindrical housing so as to form a U-shaped pattern or take the form of strings having one end closed and fixed by a fastening member of, for example, polyurethane without blocking their open ends.
Where hollow-fiber filter modules are used in treating large volumes of water on an industrial scale, the measure taken in the prior art has been to increase the number or length of the hollow fibers contained therein.
When the number of hollow fibers per unit area is increased, the throughput of water becomes greater, up to a certain point, in proportion to the number of hollow fibers used. However, if the installation density of the hollow fibers becomes too high, the throughput of water cannot be increased in proportion to the number of hollow fibers used, because the passage of water into the inner part of the bundle of hollow fibers meets with great resistance. On the other hand, when the length of the hollow fibers is increased, the throughput of water becomes greater due to the increase in the area of the membrane. However, the relationship between the internal diameter of the hollow fibers and the performance of the filter membrane indicates that, if the length exceeds a certain limit, the resistance of the flow path within the bores of the hollow fibers becomes a limiting factor and the throughput of water cannot be increased.
Nevertheless, there may be applications in which it is desired to treat large volumes of water by use of hollow-fiber filter modules of as compact design as possible. In those applications, it has been impossible to use the conventionally known types of hollow-fiber filter modules.